南华北盆地偃龙地区二叠系泥页岩微观孔隙特征及其影响因素分析

运用氩离子抛光—场发射环境扫描电子显微成像测试技术,对南华北盆地偃龙地区ZK1614井二叠系海陆交互相—陆相的泥页岩样品进行观察并获取二次电子及背散射信息。结合X射线能谱信息和JMicro Vision软件灰度识别功能,对样品矿物组成及微观孔隙特征进行定性分析和定量表征,并探讨了孔隙发育分布的影响因素。研究发现:样品主要发育的孔隙以无机矿物孔为主,孔隙类型有粒内孔、粒间孔、少量有机质孔及微裂隙;样品面孔率介于0.92%~5.53%之间,整体来看,面孔率大小与孔隙数量正相关;孔径大小介于50~2000 nm间,不同区段的孔面积对数指标与单位面积孔数量对数指标呈两段式线性关系,孔径较小时两者负相关,孔径较大时两者正相关。不同矿物对孔隙的发育有不同的控制作用,脆性矿物主要影响裂隙的发育,对孔隙的发育有一定的抑制作用;粘土矿物因构造应力、矿物相变及脱水等作用形成大量孔隙,对孔隙的发育起一定的促进作用。研究区燕山期、喜山期因构造活动形成了大量尺度较大的裂隙,裂隙的发育使岩层的渗流性能增加,促进了有机酸和地层水对矿物的溶蚀作用,相应的促进了孔隙的发育。此外,随着埋藏深度的增加,孔隙体积随着压实作用的增大而逐渐减小。

MICROSCOPIC PORE CHARACTERISTICS AND INFLUENCE FACTORS ANALYSIS OF SHALES IN PERMIAN, YANLONG AREA, SOUTHERN NORTH CHINA BASIN

Using argon ion polishing and field emission environmental scanning electron microscopy imaging testing technique, the interactive marine-continental facies and continental facies shale samples from Permian drilled in ZK1614 well in Yanlong area of southern North China Basin are scanned, and the SE and BSE information are obtained as well. Combining X-ray spectrum information with gray level recognition function of JMicroVision software, qualitative analysis and quantitative representation of the mineral composition and the characteristics of micro pores of shale samples are made, and the genesis of pore system are discussed. The research shows that the pores of shale samples are mainly inorganic mineral pores, and the pore types include intragranular pores, intergranular pores, and a small amount of organic matter pores and micro fissures. The surface porosities of samples from Permian are between 0.92%~5.53%, and surface porosities are positively correlated with the number of pores in general. With different sizes of pores, there is a two-segment linear relationship between the logarithmic index of pore area and the logarithmic index of pore number of unit area in different pore diameter interval between 50~2000 nm, and when the pore diameter is small, they are negatively correlated, when the pore diameter is large, they are positively correlated. Different minerals result in different control effects on the development of pores.Brittle minerals mainly influence the development of micro fissures and inhibit the development of pores; clay minerals, due to the actions of tectonic stress, phase transformation and dehydration of minerals, result in plenty of pores, which promote the development of pores. Besides, the differential expansion and differential dissolution of minerals could also produce pores. During the Yanshan and the Himalayan periods, large scale fractures were formed in the study area. The development of fractures increased the penetrability of the roc kstratum, which promoted the dissolution of minerals by organic acids and formation water, and it also promoted the development of pores correspondingly. Moreover, with the increase of burial depth, the pore volume decreased with the increase of compaction.